One in three men with slow-growing prostate tumours are not getting the best treatment - and could be risking their sex lives, experts warn.
There are several treatments prostate cancer patients can opt for
Men with the condition have a range of options available to them, including "watchful waiting" where doctors monitor and give no active treatment.
But other options, such as surgery or radiotherapy, cause side effects.
Professor Roger Kirby, head of urology at St George's Hospital, London, warned patients often make uninformed choices.
The condition can take many years to develop, and men often do not need to make quick decisions about which treatment to have.
Dr Kirby said many men do often regret the option they chose, and doctors often feel they should recommend the most radical treatment.
But he said that many men could take a less drastic approach with fewer life-changing side effects, such as impotence or urinary incontinence.
How to choose
In addition to "watchful waiting", men can choose to keep their cancer under control using hormone treatment.
Each treatment has different benefits and potential side effects, so what is right for each man depends on factors such as how aggressive the cancer is, how old the patient is, and what is important to him.
Research has shown that those men who take time to consider how treatments could affect their quality of life tend to feel happier about the decisions they make.
Prostate cancer is the most common cancer in men, affecting 27,000 in the UK each year and killing 10,000.
Professor Kirby said: "Currently, perhaps a third of men when confronted with locally advanced prostate cancer needlessly risk losing their sex life by making the wrong
He said there were tools which could help doctors and patients decide which treatment is best.
Professor Kirby has been involved in developing the Vitality Index - a questionnaire which ranks side effects and assesses a patient's willingness and ability to cope with them.
Details were recently presented to a meeting of the British Association of Urological Surgeons.
He said: "This new treatment aid could help men with prostate cancer and their doctors arrive at the right treatment decisions, therefore helping to maintain the sex lives and quality lives of patients and their
Dr Chris Hiley, head of policy and research at The Prostate Cancer Charity, said: "Choosing a treatment at any stage of prostate cancer can be very difficult.
"It requires a close partnership between the doctor and the man with prostate cancer, to make sure that there is the best fit between the effects on the disease, and the side effects on each man's life.
"The working of this partnership is doubly difficult when it is established at a time when the man is anxious, vulnerable and in need of reassurance.
"As a result of these difficulties, some men may not be offered choices, despite the fact that treatments vary in their side effects. This has to change.
"Men should be helped to make informed choices. It is their body, their health, under discussion."
A Department of Health spokeswoman said men with prostate cancer were being seen more quickly and are receiving better care because of extra investment.
"We recognise that patients need clear information to help them make informed decisions about their treatment.
"That is why we have set up a Coalition for Cancer Information to develop better resources for patients and we are developing a National Prostate Cancer website where patients and their families will be able to access clear and accurate information."